Production of acrylonitrile



PRODUCTION OF ACRYLONITRILE James F. Gabhett, Jr., Weymouth, and Nat C.Robertson, Wellesley, Mass, assignors, by mesne assignments, to EscambiaChemical Corporation, Pace, Fla., a Delaware corporation N Drawing.Application October 1, 1954, Serial No. 459,870

7 Claims. (Cl. 260465.3)

This invention relates to the production of chemicals and in particularto an improved process for the production of acrylonitrile. Thisapplication is, in part, a continuation of our copending applicationsSerial No. 382,199, filed September 24, 1953, and Serial No. 412,- 635,filed February 25, 1954, now abandoned.

A principal object of the present invention is to produce high yields ofacrylonitrile readily and cheaply by reacting hydrogen cyanide withacetylene in the vapor phase in the presence of an improved catalyst.

Another object of the invention is to provide an improved process of theabove type which is particularly adapted to the production of highyields of acrylonitrile with very low yields of propionitrile and otherundesirable nitriles.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process involving the seyeralsteps and the relation and the order of one or more of such steps withrespect to each of the others which are exemplified in the followingdetailed disclosure, and the scope of the application of which will beindicated in the claims. t

For a fuller understanding of the nature and objectsi of the invention,reference should be had to the fOllOW- ing detailed description. y

it is well known that acrylonitrile can be prepared by reacting hydrogencyanide with acetylene in the vapor phase in the presence of a suitablecatalyst. Many catalysts have been reported as suitable for thisreaction and include such materials as activated carbon, silica gel andsolid, porous materials, having either a high surface activity or littleor no surface activity, impregnated with alkali metal cyanides orhydroxides or mixtures of alkali metal cyanides, etc.

Generally, the use of the preferred catalysts in the presence ofappreciable quantities of hydrogen, such as when hydrogen is used as adiluent in the feed stream of acetylene, leads to considerably loweryields of acrylonitrile than are obtained with an inert diluent such asnitrogen, while the yields of undesirable nitriles and, in particular,propionitrile are substantially increased. The large increase ofpropionitrile yield in such an environment is probably due to ahydrogenation of the acrylonitrile at reaction conditions. The presentinvention is directed to obtaining high yields of acrylonitrile with lowyields of propionitrile and other undesirable nitriles, particularlywhen the reaction is carried out in the presence of appreciablequantities of hydrogen.

The process of the present invention preferably comprises the steps ofreacting a mixture of hydrogen cysnide and acetylene in the vapor phasein the presence of a porous support comprising deoxygenated charcoalwhich has been pretreated with hydrogen cyanide. The charcoal ispreferably first impregnated with from about 3% to 15% by weight of analkali metal hydroxide, cyanide or carbonate. In a preferred embodiment,the deoxygenated charcoal is impregnated with about 10% nite f StatesPatent 0 by weight of an alkali metal hydroxide, the preferred .lltalimetal hydroxide being sodium hydroxide.

In a preferred aspect of the invention, the porous support is a softwoodcharcoal due to its lower cost. This charcoal is conditioned for use asa catalyst support by heating in the range of 500 C. to 900 C. andpassing hydrogen over the heated charcoal until substantially all of theadsorbed and combined oxygen has been removed. This procedure is alsobeneficial in removing other materials, such as tars, etc., which wouldnot be desirable in the product. The resulting deoxygenated charcoal isimpregnated with an alkali metal hydroxide, cyanide or carbonate. Thedeoxygenated impregnated charcoal is then preferably treated withhydrogen cyanide at temperatures above about 500 C. Hydrogen cyanide ispassed over the heated deoxygenated charcoal until the recovery ofhydrogen cyanide in the off-gases is on the order of 80% and above.

In one preferred embodiment of the invention, high yields ofacrylonitrile are obtained by reacting a gaseous mixture of hydrogencyanide and acetylene in the presence of the preferred improved catalystat temperatures on the order of 450 C. to 700 C. and preferably betweenabout 525 C. and 600 C. In carrying out the present invention, thetemperature is controlled within the above preferred limits when thespace velocity of the gases passing through the reactor is maintainedbetween about 300 to 800 hr. (STP). Under these conditions, temperaturesin excess of 600 C. tend to increase the yields of undesirable nitriles,particularly propionitrile, while temperatures below about 525 C. tendto give undesirably low conversions of hydrogen cyanide toacrylonitrile.

A more detailed disclosure of one method of producing acrylonitrile byuse of the improved charcoal catalyst is illustrated in the followingexample which is set forth only for the purpose of illustration and isnot to be construed as limiting the invention.

Example I i115 grams of an unactivated softwood charcoal were heated, atatmospheric pressure, to a temperature of about 700 C. in a stream ofhydrogen for about 24 hours. Water and other oxygenated products formedduring the conditioning were removed. The charcoal, on completion of thehydrogenation, was found to weigh 90 grams. grams of the deoxygenatedcharcoal was then impregnated with an aqueous solution containing about7.5 grams of sodium hydroxide to provide, after drying, about 10% byweight of sodium hydroxide in the charcoal. Upon completion of thesodium hydroxide impregnation, the catalyst was heated, at atmosphericpressure, at a temperature on the order of about 550 C. .in a stream ofhydrogen cyanamide, until the-recovery of hydrogen cyanide in theofiT-gases rose to over which, in this case, was on the order of about60 minutes. A mixture of acetylene and hydrogen cyanide was passed at aspace velocity of about 540 hr.- (STP) through a Vycor reactor tubecontaining approximately 82.5 grams of the thus prepared catalyst (i.e., 75 grams of deoxygenated charcoal plus weight of sodium hydroxide).Thetube was heated and maintained by means of a molten salt bath withinthe temperature range of between ab'out'550 C. and 600 C. .The moleratio of acetylene to hydrogen cyanide was about l.'l7:=l, with theamount of acetylene in the acetylene feed stream amountingtoapproximately 7.1% and the pressure being substantially atmospheric.The remainder of the represent-ative Wulif processiacetylene stream(92.9%) consisted mainly of about 32.4% methane, 1.8% ethylene, 3.7%carbon monoxide, 6.5% nitrogen and 48.3% hydrogen. The averageconversion of hydrogen cyanide to 3 acrylonitrile of this 70.5-hour runwas 66.0% while the average yield of acrylonitrile was 81.6% based onhydrogen cyanide. There was synthesized a weight of acrylonitrile equalto about 12.1 times the weight of the deoxygenated charcoal used inpreparing the catalyst. The average yields of propionitrile andacetonitrile based on hydrogen cyanide were 6.0% and 3.2% respectively.

Either softwood or hardwood charcoals have been found to besatisfactory. However, from an economic standpoint, softwood charcoalsare preferable.

The temperature at which the unactivated charcoal is heated during thehydrogen treatment may be varied considerably. However, it is bestmaintained between 500 C. and 900 C. and preferably around 700 C. Thetime necessary to substantially deoxygenate the unactivated charcoalwill also vary, depending on such things as the type of charcoalemployed and the temperature. In general, the deoxygenation treatmenttakes more than 8 hours and preferably between about 12 and 24 hours.The deoxygenation treatment is preferably performed at substantiallyatmospheric pressure. Although the preferred reducing agent is hydrogen,other reducing agents capable of deoxygenating the unactivated charcoalmay be utilized.

The deoxygenated charcoal may be impregnated with from about 3% to 15%by weight of either an alkali metal hydroxide, cyanide or carbonate.Best results have been obtained, however, when the treated charcoal hasbeen im regnated with about by weight of the desired alkali metalhydroxide, cyanide or carbonate. In one particular aspect of theinvention, it has been found preferable to em loy a deoxy enatedcharcoal impregnated with about 10% by wei ht of an alkali metalhydroxide which is preferably sodium or potassium hydroxide. Mixtures ofalkali metal compounds may also be used.

After the deoxygenated catal st has been impregnated, it is referablytreated With hydro en cyanide. at atmospheric pressure, at tem eratureswhich are on the order of above about 500 C. The time necessary to treatthe deoxygenated catalyst with hydrogen cyanide will vary, since it isdependent on such factors as the quantity of catalyst to be treated.throu hput rate of hydrogen cyanide. etc. However. the passage of hydroen cyanide over the deoxy enated catalyst is usually continued until therecovery of hydr en cyanide in the off-gases is on the rder of 80% andabove.

The deoxv enated impregnated catalyst is preferably pretreated withhydro en c a ide since it considerably sh rtens the time to reach mximum acrylonitrile yields. This may be explained on the theory that thecatalyst thus treated will not adsorb ny a reciable qu ntities of h droen cyanide during the earlv stages of the reaction and thus there is noc m etiti e action between the catal st and the acetylene for the h droen cyanide passing throu h the re ctor. The m ximum con ersion to. andyields of. acrvlonitrile are. therefore. obtainable within a very shorttime after the start of the reaction. The h dro en cyanide catalystpretreatment. as a result of obtaining maximum acrylonitrile yieldsfaster. thus ermits more acrylonitrile to be obtained per unit of weightof catalyst employed.

The temperature range in the reactor may vary from about 450 C. to about700 C. However, it is preferably maintained between about 525 C. and 600C. when the space velocity of the gases passing through the reactor ismaintained between about 300 to 800 hr. (STP). Under these conditions,high yields of acrylonitrile are obtained while the yields ofundesirable nitriles are suppressed and substantially eliminated.Temperatures above about 600 C. at the given space velocities tend toproduce higher yields of such undesirable nitriles as propionitrile andacetonitrile at the expense of the hydrogen cyanide recovery and theyield of acrylospace velocities tend to lead to poor conversions ofhydrogen cyanide to acrylonitrile, thus making it commerciallyunattractive.

The space velocity may vary from about hr. (STP) to about 1000 hr."(STP), preferred space velocities being on the order of between about300 and 800 hr? (ST?) at reaction temperatures between about 525 C. and600 C. When the space velocity is increased above the preferred range,the temperature control may be extended over a somewhat wider range. Atspace velocities below the preferred range, a more restrictedtemperature range may be required to obtain the maximum yields ofacrylonitrile. In addition to the space velocity of the gas stream, theconcentration of hydrogen in the stream of reacting gases also, to somedegree, determines the temperature to be employed. When the reaction iscarried out in the presence of large concentrations of hydrogen (aboveabout 30% by volume of the acetylene feed stream) such as shown inExample I. then a close control on the temperature is essential so as toprevent undue hydrogenation of the product. However, t lower hydrogenconcentrations (below about 30% of the acetylene feed stream) in thestream of reacting gases, then a more extended temperature range may bepermitted.

The molar ratio of acetylene to hydrogen cyanide may be varied quitewidely between about 0.811 to about 1.6:1 and higher, preferred molarratios being on the order of between about 0.921 to 1.2:1.

In the above example, specific operating conditions have been given.These conditions, however, are subject to considerable variation withoutdeparting from the scope of the invention. For example, the pressurerange in the reactor may vary from about atmospheric pressure to about100 pounds per square inch. Other catalysts, such as oxygen-free, porouscharcoal supports impregnated with an alkali metal carbonate or cyanide,can be employed in the reaction. While the reaction has been describedas being carried out in the presence of appreciable quantities ofhydrogen, it is equally ap- ;plicable to reactions carried out in theabsence of hydrogen or in the presence of other diluents.

In the example cited above, a dilute stream of acetylene representativeof a Wulif process gas stream was employed. The above example,illustrating the use of an acetylene stream containing on the order ofabout 7% acetylene and an appreciable quantity of hydrogen, shows thathigh yields of acrylonitrile with low yields of undesired propionitrilecan be obtained in the presence of the preferred improved catalyst. Thepresence of materials such as methane, ethylene, nitrogen and carbonmonoxide in a stream of reacting gases as shown in Example I, does notmaterially affect the behavior of the catalyst in producing high yieldsof acrylonitrile. Although this invention has been described inconnection with the use of dilute acetylene streams, particularly toacetylene streams containing less than about 15% acetylene, it is alsoapplicable to concentrated acetylene streams.

Since certain changes may be made in the above process without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:

1. The process of producing acrylonitrile from hydrogen cyanide andacetylene which comprises heating unactivated charcoal to a temperatureabove 500 C., passing hydrogen over said heated charcoal untilsubstantially all the oxygen has been removed from said charcoal,impregnating said deoxygenated charcoal with a compound from the groupconsisting of the alkali metal hydroxides, cyanides and carbonates,passing hydrogen cyanide over said deoxygenated impregnated charcoalnitrile. Temperatures below about 525 C. at the given 7 h l i harcoal isheated above about 500 C. until the recovery of hydrogen cyanide in theoil-gases is above 80%, passing hydrogen cyanide and acetylene over theprepared catalyst at a temperature within the range of 450 C. to 700 C.,and recovering the acrylonitrile produced.

2. The process according to claim 1 wherein said deoxygenated charcoalis impregnated with from 3% to 15% by weight of sodium hydroxide.

3. The process according to claim 1 wherein said acetylene is a dilutestream of acetylene.

4. The process of producing acrylonitrile from hydrogen cyanide andacetylene which comprises deoxygenating a porous charcoal support,impregnating said treated charcoal with a compound from the groupconsisting of the alkali metal hydroxides, cyanides and carhon-ates,passing hydrogen cyanide over said deoxygenated impregnated charcoalwhile said charcoal is heated above about 500 C. until the recovery ofhydrogen cyanide in the off-gases is above 80%, passing hydrogen cyanideand acetylene over the prepared catalyst at a temperature within therange of 525 C. to 600 C., and recovering the acrylonitrile produced.

5. The process of producing acrylonitrile from hydrogen cyanide andacetylene which comprises deoxygenating a porous charcoal support,impregnating said treated charcoal with a compound from the groupconsisting of the alkali metal hydroxides, cyanides and carbonates,passing hydrogen cyanide over said deoxygenated impregnated charcoalwhile said charcoal is heated above about 500 C. until the recovery ofhydrogen cyanide in the off-gases is above 80%, passing acetylene andhydrogen cyanide in a molar ratio of from about 0.8: to about 1.6:1 overthe prepared catalyst at a space velocity between about 300 and 800 hl'.(STP) while said catalyst is maintained at a temperature within therange of 525 C. to 600 C., and recovering the acrylonitrile produced.

6. The process according to claim 5 wherein said porous charcoal supportis impregnated with from 3% to 15% by weight of sodium hydroxide.

7. The process according to claim 5 wherein said acetylene stream is adilute stream of acetylene.

References Cited in the file of this patent UNITED STATES PATENTS2,419,186 Harris et a1 Apr. 15, 1947 FOREIGN PATENTS 584,662 GreatBritain Jan. 20, 1947

1. THE PROCESS OF PRODUCING ACRYLONITRILE FROM HYDROGEN CYANIDE ANDACETYLENE WHICH COMPRISES HEATING UNACTIVATED CHARCOAL TO A TEMPERATUREABOVE 500*C., PASSING HYDROGEN OVER SAID HEATED CHARCOAL UNTILSUBSTANTIALLY ALL THE OXYGEN HAS BEEN REMOVED FROM SAID CHARCOAL,IMPREGANATING SAID DEOXYGENATED CHARCOAL WITH A COMPOUND FROM THE GROUPCONSISTING OF THE ALKALI METAL HYDROXIDES, CYANIDES AND CARBONATES,PASSING HYDROGEN CYANIDE OVER SAID DEOXYGENATED IMPREGNATED CHARCOALWHILE SAID CHARCOAL IS HEATED ABOVE ABOUT 500*C. UNTIL THE RECOVERY OFHYDROGEN CYANIDE IN THE OFF-GASES IS ABOVE 80%, PASSING HYDROGEN CYANIDEAND ACETYLENE OVER THE PREPARED CATALYST AT A TEMPERATURE WITHIN THERANGE OF 450*C. TO 700*C., AND RECOVERING THE ACRYLONITRILE PRODUCED.